Cutter protection during leaching process

ABSTRACT

A method of forming a thermally stable cutting element may include providing a cutting element including a substrate fixed to a polycrystalline diamond cutting table; enclosing the substrate and at least a portion of the polycrystalline diamond cutting table within a protective element to form a partially enclosed cutting element; exerting a compressive squeeze on the cutting element of about 5-25%; and exposing the partially enclosed cutting element to a leaching solution so that at least part of an unenclosed portion of the polycrystalline diamond table is in contact with the leaching solution.

This Application claims the benefit of U.S. Provisional Application 61/845,774 filed on Jul. 12, 2013 and U.S. Provisional Application 61/921,165 filed on Dec. 27, 2013, both of which are herein incorporated by reference in their entirety.

BACKGROUND

Polycrystalline diamond compact (“PDC”) cutters have been used in industrial applications including rock drilling and metal machining for many years. Generally a compact of polycrystalline diamond (PCD) (or other superhard material) is bonded to a substrate material, which is a sintered metal-carbide to form a cutting structure. PCD includes a polycrystalline mass of diamonds (generally synthetic) that are bonded together to form an integral, tough, high-strength mass or lattice. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired.

A PDC cutter may be formed by placing a cemented carbide substrate into the container of a press. A mixture of diamond grains or diamond grains and catalyst binder is placed atop the substrate and treated under high pressure, high temperature conditions. In doing so, metal binder (often cobalt) migrates from the substrate and passes through the diamond grains to promote intergrowth between the diamond grains. As a result, the diamond grains become bonded to each other to form the diamond layer, and the diamond layer is in turn bonded to the substrate. The substrate often includes a metal-carbide composite material, such as tungsten carbide. The deposited diamond layer is often referred to as the “diamond table” or “abrasive layer.”

Conventional PCD includes 85-95% by volume diamond and a balance of the binder material, which is present in PCD within the interstices existing between the bonded diamond grains. Binder materials that are generally used in forming PCD include Group VIII elements, with cobalt (Co) being the most common binder material used. The binder material is often removed to improve the thermal stability of the PDC cutter.

SUMMARY

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

In one aspect, embodiments disclosed herein relate to a method of treating a cutting element that includes providing a cutting element including polycrystalline diamond fixed to a substrate; enclosing the substrate and at least a portion of the polycrystalline diamond within a protective element to form a partially enclosed cutting element; exerting a compressive squeeze on the cutting element of about 5-25%; and exposing the partially enclosed cutting element to a leaching solution so that at least part of an unenclosed portion of the polycrystalline diamond is in contact with the leaching solution.

In another aspect, embodiments disclosed herein relate to a protected cutting element that includes a cutting element including polycrystalline diamond fixed to a substrate; and a protective element enclosing the substrate and at least a portion of the polycrystalline diamond and exerting a compressive squeeze of about 5-25% on the cutting element.

In yet another aspect, embodiments disclosed herein relate to a method of treating a cutting element that includes providing a cutting element including polycrystalline diamond attached to a substrate; enclosing the substrate and at least a portion of the polycrystalline diamond within a protective element including at least one FFKM perfluoroelastomeric material to form a partially enclosed cutting element; and exposing the partially enclosed cutting element to a leaching solution so that at least part of an unenclosed portion of the polycrystalline diamond is in contact with the leaching solution.

Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustration of a PDC drill bit.

FIG. 2 is a cross-section of a partially enclosed cutting element formed by coating with a curable liquid.

FIG. 3 is a cross-section of an embodiment of a partially enclosed cutting element within a pre-molded sleeve.

FIG. 4 is a cross-section of an embodiment of a partially enclosed cutting element within a pre-molded sleeve with a substantially thicker area of sleeve located near an area adjacent the interface of the molded sleeve and the uncovered portion of the polycrystalline diamond table.

FIG. 5 is a cross-section of an embodiment of a partially enclosed cutting element enclosed within an inert housing protective element which utilizes an o-ring as the sealing element to secure the substrate and at least a portion of the polycrystalline diamond table therein.

FIG. 6 is a perspective illustration of a protected cutting element.

FIG. 7-1 is a cross sectional illustration of a protected cutting element.

FIG. 7-2 depicts a section of FIG. 7-1.

FIG. 8-1 is a side cutaway of one embodiment depicting an interference fit between a cutting element and a protective element.

FIG. 8-2 is a side cutaway of one embodiment depicting an interference fit between a cutting element and a protective element.

FIG. 8-3 is a side cutaway of one embodiment depicting an interference fit between a cutting element and a protective element.

FIG. 8-4 is a side cutaway of one embodiment depicting an interference fit between a cutting element and a protective element.

FIG. 8-5 is a side cutaway of one embodiment depicting an interference fit between a cutting element and a protective element with a flange having an embedded ring.

FIG. 8-6 is a side cutaway of one embodiment depicting an interference fit between a cutting element and a protective element with a flange and a snap ring.

FIG. 8-7 is a side cutaway of one embodiment depicting an interference fit between a cutting element and a protective element with a flange and an snap ring with extended length.

DETAILED DESCRIPTION

Leaching of intact cutting elements with an acid (or a mixture of acids, such as a mixture of HF and HNO₃) may remove catalyst from the substrate. Such treatments tend to take time, for example, several weeks, which puts substantial demands on the types of materials that can be utilized to protect the vulnerable parts of cutting element from the acidic and corrosive nature of a leaching solution. To expedite leaching, cutting elements exposed to an acidic leaching solution may also be exposed to heat. Under these harsh conditions, protective materials may embrittle, swell, degrade, or otherwise experience changes in properties resulting in failure, which may lead to irreversible damage to the cutting elements (e.g., damage to the substrate) or to dangerous exposure to leaching solutions for those handling the cutting elements during and after the leaching process.

In one aspect, embodiments disclosed herein relate to methods of leaching cutting elements containing a polycrystalline diamond body. More particularly, embodiments disclosed herein relate to protective methods and elements for the protection of regions of a cutting element which are not desired to be exposed to a leaching solution during a leaching process. Specific embodiments described may serve to concentrate the contact sealing forces between the protective element and the cutting element to minimize the potential of leaching solution ingress past the seal surfaces during the leaching process (or past a particular part of the seal during the leaching process). Further, the design features expressed in some embodiments may also improve the useful service life of the protective element during the leaching process. These protective methods and elements can be used in conjunction with conventional leaching protocols including those involving accelerating techniques such as elevated temperatures, pressures, and/or the use of ultrasound.

Forming Polycrystalline Diamond

A polycrystalline diamond body may be formed in a conventional manner, such as by a high pressure, high temperature sintering of “green” particles to create intercrystalline bonding between the particles. “Sintering” may involve a high pressure, high temperature (HPHT) process. To form the polycrystalline diamond body, an unsintered mass of diamond crystalline particles is placed within a metal enclosure of the reaction cell of a HPHT apparatus. A metal catalyst, such as cobalt or other Group VIII metals, may be included with the unsintered mass of crystalline particles to promote intercrystalline diamond-to-diamond bonding, may be included adjacent to the unsintered mass of crystalline particles, or may be provided from the substrate. The catalyst material may be provided in the form of powder and mixed with the diamond grains, or may be infiltrated into the diamond grains during HPHT sintering. An example minimum temperature is about 1200° C. and an example minimum pressure is about 35 kilobars. Generally, processing may occur at a pressure of about 45 kbar and 1300° C. Those of ordinary skill in the art will appreciate that a variety of temperatures and pressures may be used, and the scope of the present disclosure is not limited to specifically referenced temperatures and pressures.

Diamond grains useful for forming a polycrystalline diamond body may include any type of diamond particle, including natural or synthetic diamond powders having a wide range of grain sizes. For example, such diamond powders may have an average grain size in the range from submicrometer in size to 100 micrometers, and from 1 to 80 micrometers in other embodiments. Further, one skilled in the art would appreciate that the diamond powder may include grains having a mono- or multi-modal distribution.

The diamond powder may be combined with the desired catalyst material, and the reaction cell may then be placed under processing conditions sufficient to cause intercrystalline bonding between the diamond particles. If too much additional non-diamond material is present in the powdered mass of crystalline particles, appreciable intercrystalline bonding may be prevented during the sintering process. Such a sintered material where appreciable intercrystalline bonding has not occurred is not within the definition of PCD. Following such formation of intercrystalline bonding, a polycrystalline diamond body may be formed that has, in some embodiments, at least about 80 percent by volume diamond, with the remaining balance of the interstitial regions between the diamond grains occupied by the catalyst material. In other embodiments, such diamond content may include at least 85 percent by volume of the formed diamond body, and at least 90 percent by volume in yet other embodiments. However, one skilled in the art would appreciate that other diamond densities may be used in other embodiments. Thus, the polycrystalline diamond bodies being leached in accordance with the present disclosure include what is frequently referred to in the art as “high density” polycrystalline diamond. One skilled in the art would appreciate that conventionally, as diamond density increases, the leaching time (and potential inability to effectively leach) similarly increases.

Further, one skilled in the art would appreciate that, frequently, a diamond layer is sintered to a carbide substrate by placing the diamond particles on a preformed substrate in the reaction cell and sintering. However the present disclosure is not so limited. Rather, the polycrystalline diamond bodies treated in accordance with the present disclosure may or may not be attached to a substrate.

In some embodiments, the polycrystalline diamond body may be formed using solvent catalyst material provided as an infiltrant from a substrate, for example, a WC—Co substrate, during the HPHT process. In such embodiments where the polycrystalline diamond body is formed with a substrate, it may be desirable to remove the polycrystalline diamond portion from the substrate prior to leaching so that leaching agents may attack the diamond body in an unshielded manner, i.e, from each side of the diamond body without substantial restriction.

Further, one skilled in the art would appreciate that the same techniques used with polycrystalline diamond may be applied to polycrystalline cubic boron nitride (PCBN). Similar to polycrystalline diamond, PCBN may be formed by sintering boron nitride particles (often CBN) via a HPHT process, similar to those for PCD, to sinter “green” particles to create intercrystalline bonding between the particles. CBN refers to an internal crystal structure of boron atoms and nitrogen atoms in which the equivalent lattice points are at the corner of each cell. Boron nitride particles generally have a diameter of approximately one micron and appear as a white powder. Boron nitride, when initially formed, has a generally graphite-like, hexagonal plate structure. When compressed at high pressures (such as 106 psi), CBN particles will be formed with hardness very similar to diamond, and stability in air at temperatures of up to 1400° C.

According to some embodiments, PCBN may include a content of boron nitride of at least 50% by volume; at least 70% by volume in other embodiments; at least 85% by volume in yet other embodiments. In other embodiments, the cubic boron nitride content may range from 50 to 80 percent by volume, and from 80 to 99.9 percent by volume in yet other embodiments. The residual content of the polycrystalline cubic boron nitride composite may include at least one of Al, Si, and mixtures thereof, carbides, nitrides, carbonitrides and borides of Group IVa, Va, and VIa transition metals of the periodic table. Mixtures and solid solutions of Al, Si, carbides, nitrides, carbonitrides and borides of Group IVa, Va, and VIa transition metals of the periodic table may also be included.

An example of a rock bit for earth formation drilling using PDC cutters is shown in FIG. 1. FIG. 1 shows a rotary drill bit 10 having a bit body 12. The lower face of the bit body 12 is formed with a plurality of blades 14, which extend generally outwardly away from a central longitudinal axis of rotation 16 of the drill bit. A plurality of PDC cutters 18 are disposed side by side along the length of each blade. The number of PDC cutters 18 carried by each blade may vary. The PDC cutters 18 are individually brazed and are received and secured within sockets in the respective blade.

A factor in determining the longevity of PDC cutters is the generation of heat at the cutter contact point, specifically at the exposed part of the PDC layer caused by friction between the PCD and the work material. This heat causes thermal damage to the PCD in the form of cracks (due to differences in thermal expansion coefficients) which lead to spalling of the polycrystalline diamond layer, delamination between the polycrystalline diamond and substrate, and back conversion of the diamond to graphite causing rapid abrasive wear. The thermal operating range of conventional PDC cutters is generally 750° C. or less.

As mentioned, conventional polycrystalline diamond is stable at temperatures of up to 700-750° C., after which observed increases in temperature may result in permanent damage to and structural failure of polycrystalline diamond. This deterioration in polycrystalline diamond may be due to the difference in the coefficient of thermal expansion of the binder material, cobalt, as compared to diamond. Upon heating of polycrystalline diamond, the cobalt and the diamond lattice will expand at different rates, which may cause cracks to form in the diamond lattice structure and result in deterioration of the polycrystalline diamond. Damage may also be due to graphite formation at diamond-diamond necks leading to loss of microstructural integrity and strength loss.

In order to overcome this problem, strong acids may be used to “leach” the cobalt from the diamond lattice structure (either a thin volume or entire tablet) to at least reduce the damage experienced from heating the diamond-cobalt composite. Briefly, a strong acid, such as nitric acid or combinations of several strong acids (such as nitric and hydrofluoric acid) may be used to treat the diamond table, removing at least a portion of the catalyst from the PDC composite. By leaching out the cobalt, thermally stable polycrystalline (TSP) diamond may be formed. In certain embodiments, a select (less than all) portion of a diamond composite is leached, in order to gain thermal stability without losing impact resistance. As used herein, the term TSP includes both of the above (i.e., partially and completely leached) compounds. Interstitial volumes remaining after leaching may be reduced by either furthering consolidation or by filling the volume with a secondary material.

However, it is highly undesirable for the substrate of a cutting element including a

PCD cutting table to be exposed to the leaching solution. Exposure of the substrate to the leaching solution can weaken both the structural integrity of the substrate itself, along with the interfacial bond attaching the PCD cutting table to the substrate. This vulnerability has led to leaching processes being performed with unattached PCD cutting tables, which then require attachment/re-attachment to a substrate via brazing or high-temperature high-pressure sintering. The attachment/re-attachment of TSP cutting tables may lead to weak interfacial attachment. Leaching processes may also use protection methods for the substrate of intact (with substrate bonded to cutting table) cutting elements. Furthermore, while shear cutters are described throughout the text and shown in the figures, in some embodiments, the leaching methods and protective elements described in this disclosure may also be used with any other type of cutting element that could benefit from leaching.

Leaching Process

In various embodiments, a formed PCD body having a catalyst material or other metal in the interstitial spaces between bonded diamond grains is subjected to a leaching process in conjunction with at least one protective element, whereby the catalyst material or other metal is at least partially removed from the PCD body. In addition to the catalyst material that may be removed by a leaching process, it is also within the scope of the present disclosure that the present disclosure also relates to the leaching of a metal infiltrant that may occupy the interstitial spaces when a preformed PCD body is attached to a substrate during a subsequent HPHT sintering process, thereby infiltrating a metal from the substrate into the preformed body. As used herein, the term “removed” refers to the reduced presence of catalyst material or other metal in the PCD body, and is understood to mean that a substantial portion of the catalyst material no longer resides in the PCD body. However, one skilled in the art would appreciate that trace amounts of catalyst material or other metal may still remain in the microstructure of the PCD body within the interstitial regions and/or adhered to the surface of the diamond grains.

The quantity of the catalyst material or other metal remaining in the material PCD microstructure after the PCD body has been subjected to a leaching treatment may vary, for example, on factors such as the treatment conditions, including treatment time. Further, one skilled in the art would appreciate that it may be desired in certain applications to allow a small amount of catalyst material or other metal to stay in the PCD body. In some embodiments, the PCD body may include up to 1-2 percent by weight of the catalyst material or other metal. However, one skilled in the art would appreciate that the amount of residual catalyst or other metal present in a leached PCD body may depend on the diamond density of the material, and body thickness.

As described above, a conventional leaching process involves the exposure of an object to be leached with a leaching agent. In select embodiments, the leaching agent may be a weak, strong, or mixtures of acids. In other embodiments, the leaching agent may be a caustic material such as NaOH or KOH. Suitable acids may include, for example, nitric acid, hydrofluoric acid, hydrochloric acid, sulfuric acid, phosphoric acid, or perchloric acid, as well as any organic acids (such as formic, lactic, oxalic, citric, or acetic acid), or combinations of these acids. In addition, other acidic and basic leaching agents may be used as desired. Those having ordinary skill in the art will appreciate that the molarity of the leaching agent may be adjusted depending on the time desired to leach, concerns about hazards, etc.

Additionally, in select embodiments, accelerating techniques may be applied to the leaching process to decrease the amount of treatment time to reach the same level of catalyst or other metal removal. In some embodiments, the leaching of a PCD body may be accelerated by subjecting the leaching environment and thus the PCD body to an elevated pressure. As used herein, the term “elevated pressure” refers to pressures greater than atmospheric pressure. Suitable pressure levels may include elevated pressure levels ranging from about 5 to 345 bar, and ranging from about 5 to 100 bar in other embodiments. However, one skilled in the art would appreciate that the particular pressure may be dependent, for example, on the particular equipment used, the temperature selected, amount (and type) of leaching agent present, and total system volume. Additionally, in one or more embodiments, the temperature of the leaching agent may be increased relative to ambient temperature during the leaching process to a temperature up to about the boiling point of the leaching solution. In yet other embodiments, the temperature of the leaching agent may be up to three times the boiling point of the leaching solution. Further, in one or more embodiments, the application of ultrasonic energy to accelerate the leaching process may be used. Ultrasonic energy is mechanical, vibratory energy in the form of sound that operates at frequencies beyond audible sound (18,000 cycles per second and greater). An ultrasonic stack is generally formed of a converter or piezoelectric transducer, an optional booster and a sonotrode (also called a horn).

In one or more embodiments, the substrate of the cutting element and at least a portion of the polycrystalline diamond cutting table may be enclosed by a protective element. The protective element may be configured to allow for the protection of the substrate and at least a portion of the polycrystalline diamond cutting table of a cutting element from exposure to an external leaching environment, by placing, for example, a compressive squeeze on the cutting element. Such a protective element may include at least one of an o-ring seal, a snap ring, or a “sleeve”, for example. In particular embodiments, the protective elements may include two or more components: one to partially enclose the cutting element and a second to exert a compressive squeeze on the cutting element. In some embodiments, the enclosure and the compressive squeeze may be achieved by a single component. In embodiments using two components, an elastomeric material may be used as one of the materials and a thermoplastic polymer, such as polypropylene (PP), polyethylene (PE), high density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMWPE), cross-linked polyethylene (PEX), polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) may be used as the other.

Due to the chemical composition of the leaching solutions, it may be beneficial for protective elements to include one or more thermoset elastomers or halogen containing polymers. However, the present disclosure is not limited and in one or more embodiments, polymers which may be useful in the material composition of a protective element may be at least one material from FKM fluoroelastomers, tetrafluoroethylene/propylene copolymers, polychloroprene, chlorinated polyethylene, chlorosulfonated polyethylene, epichlorohydrin, fluorosilicone, hydrofluorocarbon, fluoroelastomers, halobutyl elastomers, polypropylene, polyethylene, polyvinylidene fluoride, polytetrafluoroethylene, a liquid crystal polymer, polyetherketone, high density polyethylene, ultra high molecular weight polyethylene, cross-linked polyethylene, and/or FFKM perfluoroelastomers. These may be used alone or in combination to achieve the desired performance when exposed to leaching solutions.

Changes in physical properties such as volume swell, loss of tensile strength, loss of elongation, stress relaxation, permanent set and changes in hardness, etc. may be reduced through proper selection of the base polymer, including blends of polymers, sometimes referred to as alloys, and proper selection of fillers, cure systems and other additives. In addition to the material composition, the design of the protective element may take these physical property changes into consideration so that an effective seal and consistent sealing surface can be maintained throughout the leaching process. Specific embodiments described in the present disclosure concentrate the contact sealing forces between the protective element and the cutting element to minimize or reduce the potential of acid ingress past the seal surfaces during the leaching process. These design features may also significantly improve the useful service life of the protective element during the leaching process.

FFKM perfluoroelastomers are differentiated from FKM fluoroelastomers, a class within which VITON® is included, in that FFKM perfluoroelastomers have a fully fluorinated polymer backbone and thus a greater weight percentage of the elastomer is made up of fluorine. This difference imparts a higher resistance to degradation brought on by high temperatures and/or reactive chemicals. In general, FFKM perfluoroelastomers are copolymers of tetrafluoroethylene (TFE), which is the precursor to polytetrafluoroethylene (PTFE) or TEFLON®, and polymethylvinylether (PMVE) or other poly(alkyl vinyl ethers) or poly(alkoxy vinyl ethers). At least one cure site monomer, with the monomer having a functional group to promote curing, may also be incorporated therein to permit crosslinking of the curable polymer. Further, other polyalkylvinylethers (PAVEs) may be used to make FFKM perfluoroelastomers and include those with alkyl or alkoxy groups that may be straight or branched and which may also include ether linkages such as polyethylvinylether (PEVE), polypropylvinylether (PPVE), and polymethoxy vinylether, or other monomers represented by the following formula: CF₂═CFO(R_(f)—O)_(n)(R_(f′)—O)_(m)R_(f″) where R_(f) and R_(f′) are different linear or branched perfluoroalkylene groups of 2-6 carbon atoms, m and n are independently 0 or 1, and R_(f″) is a perfluoroalkyl group of 1-6 carbon atoms. Mixtures of the different PAVEs may also be used. In one or more embodiments, the amount of PAVE monomer in the FFKM perfluoroelastomer may be from about 15-65 mol %.

Examples of the cure site functionality may include nitrogen containing groups (such as nitrile or cyano), carboxyl groups, and/or alkoxy carbonyl groups. Such functional groups may be provided on a fluorinated olefin or fluorinated vinylether. It is within the scope of the present disclosure that the cure site monomer may be partially or fully fluorinated. In one or more embodiments, the amount of cure site functionality in the FFKM perfluoroelastomer may be from 0.1-5 mol %.

Further, it is also within the scope of the present disclosure that other perfluoro olefins, such as hexafluoropropylene (HFP) may be used in place of or admixed with TFE in the FFKM perfluoroelastomer. In one or more embodiments, the perfluoro olefins may account for the balance or about 35 mol % in the FFKM perfluoroelastomer.

In embodiments using FKM fluoroelastomers, monomers may include hexafluoropropylene (HFP), vinylidene fluoride (VF2/VDF), terfluoroethylene (TFE), a fluorinated vinyl ether (PMVE). In particular embodiments, the FKM elastomer may be one of Type 1, Type 2, or Type 3. Copolymers derived from the polymerization of VF2 and HFP, are broadly defined as a FKM type 1, and generally have a fluorine content by weight of approximately 66%. In FKM type 2, termed a terpolymer, the TFE addition to the monomer composition variably increases the fluorine content between 67% and 70%, depending on the polymer grade. A FKM type 3 is generally composed of VF2, TFE, and PMVE. At least one cure site monomer, with the monomer having a functional group to promote curing, such as those described above, may also be incorporated therein to permit crosslinking of the curable polymer.

In some embodiments, the substrate and at least a portion of the polycrystalline diamond table of the cutting element may be coated with a curable liquid including one of the above described elastomer materials. The coating on the cutting element may be formed by any means known in the art, although dipping the cutting element within the curable liquid, or spray-coating the cutting element with the curable liquid may be used. In one or more embodiments, prior to coating the substrate and at least a portion of the polycrystalline diamond table of the cutting element at least a portion of the polycrystalline diamond table may be masked with a masking material to prevent it from being coated with the curable liquid. The mask may allow for easier application and/or specific patterning of the curable liquid. After coating the cutting element, the curable material may be cured according to known teachings in elastomers, to form a sleeve in-situ. In one or more embodiments, the masking material may be removed after the coating with the curable liquid and prior to the exposure of the partially enclosed cutting element to the leaching solution. In other embodiments, the masking material may be retained on the cutting element and substantially degraded during the leaching process. A cross-section of a resultant partially enclosed cutting element 20 is shown in FIG. 2 showing the fully enclosed substrate 20, partially exposed polycrystalline diamond table 22, and the surrounding protective element 24.

In one or more other embodiments, the substrate and at least a portion of the polycrystalline diamond table may be enclosed within a protective element by inserting a portion of the cutting element into a pre-molded sleeve made of one of the above described elastomer materials. The pre-molded sleeve may possess substantially the same dimensions as the portion of the cutting element to be enclosed or may possess slightly smaller dimensions than the portion of the cutting element to be enclosed. Specifically, in one or more embodiments, the diameter of the molded sleeve may be less than the diameter of the substrate and polycrystalline diamond table. The smaller diameter of the pre-molded sleeve may allow for an interference fit between the pre-molded sleeve and the enclosed portion of the cutting element leading to the exertion of a compressive squeeze on the enclosed portion of the cutting element which may increase the degree of protection provided by the sleeve. Additionally, the pre-molded sleeve may be engineered so that the degree of compressive squeeze exerted on the enclosed portion at an area adjacent the interface of the molded sleeve and the uncovered portion of the polycrystalline diamond table is higher than at an area not adjacent the interface. This type of engineering may take the form of a bulge or substantially thicker area of sleeve made of one of the above described materials located near an area adjacent the interface of the molded sleeve and the uncovered portion of the polycrystalline diamond table. In one or more embodiments, the compressive squeeze exerted at any point on the enclosed portion of the cutting element may range from about 5% to 25%, 10% to 20%, or at least 5%, 10%, 15%, 20%, or 25% in other embodiments.

FIG. 3 shows a cross-section of an embodiment of a partially enclosed cutting element 20 within a pre-molded sleeve where the fully enclosed substrate 20, partially exposed polycrystalline diamond table 22, a pre-molded sleeve 30 are illustrated. FIG. 4 shows a cross-section of an embodiment of a partially enclosed cutting element 20 within a pre-molded sleeve with a substantially thicker area of sleeve located near an area adjacent the interface of the molded sleeve and the uncovered portion of the polycrystalline diamond table where the fully enclosed substrate 20, partially exposed polycrystalline diamond table 22, a pre-molded sleeve 30, and substantially thicker area of sleeve 40 are illustrated. In one or more embodiments, the pre-molded sleeve may have a thickness, at its opening that receives a cutting element and is adjacent the interface of the sleeve and the uncovered portion of the polycrystalline diamond table, that is at least 1.25 times the thickness at the distal end of the sleeve. In one or more other embodiments, such thickness adjacent the opening may be at least 1.5, 2.0, or 2.5 times the thickness of the distal end or up to 5 times the thickness in yet other embodiments.

Shown in FIG. 6, an interference fit between a protective element, in this instance a sleeve 30, and a cutting element 62 disposed therein may be achieved thereby resulting in hoop tension stresses 60 adjacent the opening of the sleeve. Hoop tensile stresses 60 are induced in the sleeve 30 when the cutting element 62 is disposed therein. An interference fit may be achieved or even enhanced by other embodiments described below. For example, FIG. 8-1 illustrates one embodiment where the inside diameter of the protective element, sleeve 30, is slightly smaller than the outside diameter of the cutting element 62 to be inserted to create an interference fit 90. During insertion of the cutting element 62, the sleeve 30 is loaded in hoop tension due to the expansion of the sleeve 30 around the slightly larger cutting element 62. The degree of interference may be sufficient to overcome the amount of positive volume change that may be experienced by the sleeve 30 during the leaching process in order to maintain the requisite level of contact sealing force and prevent or reduce leaching solution ingress. The hoop tensile stress is relaxed if the sleeve 30 swells upon exposure to the leaching solution during the leaching process. In one or more embodiments, volume changes due to swelling of the sleeve 30 may be no more than 5% to 20% and the initial degree of interference may be sufficient to overcome this change to maintain a sufficient contact sealing force from the hoop tensile stress.

FIG. 8-2 illustrates an embodiment wherein the inside diameter of the sleeve 30 may be tapered to concentrate the hoop tensile stress from the interference fit at the open end of the sleeve 30 in order to prevent or reduce leaching solution ingress. Utilizing a design such as this may allow for less force to be used during the insertion of a cutting element 62 into the sleeve 30, while still providing for a sufficient degree of interference to account for any swelling of the sleeve 30 that may occur during the leaching process. This embodiment and others may use an initial pretension hoop stress with the protective element, sleeve 30, to offset the effects of stress relaxation and positive volume change due to any swelling of the elastomer during exposure to the leaching solution.

FIG. 8-3 illustrates an embodiment where the inside surface of the protective element, sleeve 30, has a raised sealing surface which serves to concentrate the contact sealing force near the open end of the protective element in order to prevent or reduce leaching solution ingress. In some embodiments there may be more than one raised sealing surface within the protective element and the one or more raised sealing surface may be located near the opening of the sleeve 30 or may be located a distance above the opening on the inside of the sleeve, e.g., to correspond to the location of a snap ring described below. The raised sealing surface may be an integral part of the protective element itself or it may be an o-ring fitted into a groove within the protective element. In one or more embodiments, the raised sealing surface may be made of substantially the same materials as the protective element or a dissimilar material composition. Utilizing a design such as this may allow for less force to be used during the insertion of a cutting element 62 into the protective element, while providing for a well-defined sealing surface and still providing for a sufficient degree of interference to account for any swelling of the protective element or o-ring that may occur during the leaching process.

FIG. 8-4 illustrates an embodiment of a protective element, sleeve 30, where an outwardly projecting flange is located near the open end of the protective element. The increased thickness of the outwardly projecting flange may increase the hoop tensile stress in this area of the protective element and in turn concentrate the contact sealing forces upon the insertion of a cutting element 62. In some embodiments, the protective sleeve 30 and the flange may be made of substantially the same material composition and be formed integrally, while in other embodiments a polymer with a higher modulus may be used for the flange region of the protective cutting element to further increase the hoop tensile stress and contact sealing force in the flange region.

FIG. 8-5 illustrates a protective element, sleeve 30, similar to that shown in FIG. 8-4 with the addition of a much stiffer material 92, such as a steel or polymeric ring, embedded within the outwardly projecting flange or within the annular space defined by the interior and exterior surface of the protective element. The potential expansion of the protective element when exposed to the leaching solution may be substantially restricted by using the semi-rigid or rigid embedded ring 92. The embedded ring 92 serves to pre-compress the protective element against the inserted cutting element 62 rather than allowing the protective element to be pre-tensioned upon insertion of the cutting element 62. The pre-compression may help to counteract the effect of the positive volume change of the protective element due to swelling in the presence of the leaching solution. FIG. 7-2 illustrates the hoop or tangential compression 60 and radial compression 74 stresses due to the interference fit between the protective element, in this instance sleeve 30, and the cutting element 62 when a stiffer reinforcing material, in this instance snap ring 70, is used as a component of the protective element. In the embodiment shown in FIGS. 7-1 and 7-2, hoop or tangential compression 60 directed around the perimeter of the sleeve 30 and cutting element 62 may result from the interference fit of the cutting element 62 into the sleeve 30, while radial compression stress 74 directed inwardly onto the sleeve 30 and cutting element 62 may result from the snap ring when it is emplaced around the sleeve 30 and cutting element 62. Also illustrated in FIG. 7-1, when a stiffer reinforcing material is used as a component of the protective element, contact sealing forces 72 may be concentrated in the area around the interface of the protective element having the stiffer reinforcing material and the cutting element.

FIG. 8-6 illustrates a protective element, sleeve 30, similar to that shown in FIG. 8-5 where a semi-rigid or rigid snap ring 70 is used as a sealing element to generate a compressive strain when the cutting element 62 is inserted into the mask. In the configuration shown, with the snap ring 70 on the outer surface of the sleeve 30, the sleeve 30 can be engineered to have a slight amount of interference (i.e., a smaller difference in the inner diameter of the elastomeric mask or sleeve than the outer diameter of the cutting element 62) with the outer diameter of the cutting element 62 since the snap ring 70 can provide a large amount of compressive contact sealing force to prevent or reduce leaching solution ingress. In some embodiments, the cutting element 62 may be inserted into the opening of the sleeve 30 and, once the cutting element 62 is properly positioned, the snap ring 70 may then be forced down into a mating groove formed within the sleeve 30 to provide compressive contact sealing force. The dimensions of the sleeve opening and the snap ring 70 are such that a high level of compression stress may be concentrated onto the portion of the sleeve 30 and the cutting element 62 therein where the snap ring 70 is locked in place.

In one or more embodiments, a snap ring sealing element 70, whether embedded within the elastomeric sleeve 30 portion of the protective element or located on the outside of the sleeve 30, may include at least one thermoplastic material such as polypropylene, polyethylene, polyvinylidene fluoride, polytetrafluoroethylene, high density polyethylene, ultra high molecular weight polyethylene, or cross-linked polyethylene. The snap ring 70 may be reinforced with appropriate fillers to increase the resistance to stress relaxation and to increase their stiffness. In some embodiments, the resistance of a snap ring 70 to radial expansion and stress relaxation due to installation stress may be high and upon exposure to the leaching solution the volume change of the snap ring 70 may be substantially lower than the volume change of the protective element.

FIG. 8-7 illustrates a modified version of the protective element, sleeve 30, shown in FIG. 8-6 in which a snap ring sealing element 70 is configured to further increase the contact sealing force of the protective element to the cutting element 62. The snap ring 70 is similarly located within a circumferential groove around the outside of the protective element and has an extended length and goes around the flange, which may help to increase the radial interference between the outer surface of the protective element and the inner surface of the extended length of the snap ring 70.

In yet other embodiments, the substrate and at least a portion of the polycrystalline diamond table may be enclosed within a protective element by securing the substrate and at least a portion of the polycrystalline diamond table within an inert housing by a sealing element including one of the above described materials. In such embodiments, the sealing element may be an o-ring made of FFKM perfluoroelastomeric materials or one of the other elastomeric materials described above. In one or more embodiments, the o-ring may exert a compressive squeeze ranging from about 5 to 25%, or at least 5%, 10%, 15%, 20%, or 25% in other embodiments. In one or more embodiments, the inert housing may be made of an FFKM perfluoropolymer, an FKM fluoropolymer i.e., KYNAR®, or a PTFE fluoropolymer i.e., TEFLON®, or combinations thereof fabricated to accommodate the substrate and at least a portion of the polycrystalline diamond cutting table therein. The inert housing may be configured to utilize an o-ring as the sealing element to secure the substrate and at least a portion of the polycrystalline diamond table therein. FIG. 5 shows an embodiment of this configuration where the partially enclosed cutting element 20 is enclosed within an inert housing protective element 52 which utilizes an o-ring 50 as the sealing element to secure the substrate 22 and at least a portion of the polycrystalline diamond table 24 therein.

In one or more embodiments, a magnetic component may be disposed within the protective element, and magnetism may be utilized to suspend the partially enclosed cutting element in the leaching solution. Specifically, the magnetic component may be disposed within the protective element between the backface of the cutting element (e.g., the top surface of the substrate 22) and the protective element so that it is positioned directly opposite that of the exposed surface to be leached and may interact with another magnetic component outside of the protective element to suspend the protected cutting element. This suspension may allow for a more efficient and controlled packing of a plurality of the partially enclosed cutting elements in the leaching solution while also exposing the entirety of their exposed surfaces to the leaching solution. In one or more embodiments, the magnetic component may be embedded within the protective element. In one or more other embodiments, the partially enclosed cutting element may be leached within a leaching solution unsuspended with the polycrystalline diamond table faced downward or faced upwards.

Additionally, it may be desirable to combine any of the embodiments disclosed above with subjecting the partially enclosed cutting element to a temperature from about the boiling point of the leaching solution to three times the boiling point of the leaching solution. Further, it may be desirable to expose the partially enclosed cutting element to the leaching solution under elevated pressure and/or ultrasonic conditions.

Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from this disclosure. Accordingly, all such modifications are intended to be included within the scope of this disclosure. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function. 

What is claimed is:
 1. A method of treating a cutting element, comprising: providing a cutting element comprising polycrystalline diamond fixed to a substrate; enclosing the substrate and at least a portion of the polycrystalline diamond within a protective element to form a partially enclosed cutting element; exerting a compressive squeeze on the cutting element of about 5-25%; and exposing the partially enclosed cutting element to a leaching solution so that at least part of an unenclosed portion of the polycrystalline diamond is in contact with the leaching solution.
 2. The method of claim 1, wherein enclosing the substrate and at least a portion of the polycrystalline diamond within a protective element comprises inserting a portion of the cutting element into a pre-molded sleeve.
 3. The method of claim 2, wherein the exerting comprises securing the substrate and at least a portion of the polycrystalline diamond cutting within the pre-molded sleeve with at least one snap ring.
 4. The method of claim 1, wherein the protective element comprises at least one material selected from the group consisting of FKM fluoroelastomers, polychloroprene, chlorinated polyethylene, chlorosulfonated polyethylene, epichlorohydrin, fluorosilicone, hydrofluorocarbon, fluoroelastomers, halobutyl elastomers, and FFKM perfluoroelastomers.
 5. The method of claim 1, wherein enclosing the substrate and at least a portion of the polycrystalline diamond within a protective element comprises coating the substrate and at least a portion of the polycrystalline diamond table with a curable liquid composition.
 6. The method of claim 1, wherein enclosing the substrate and at least a portion of the polycrystalline diamond within a protective coating comprises securing the substrate and at least a portion of the polycrystalline diamond table within an inert housing by a sealing element.
 7. The method of claim 4, wherein prior to coating the substrate and at least a portion of the polycrystalline diamond with a curable liquid to form a coating thereon, at least a portion of the polycrystalline diamond is masked with a masking material to prevent being coated with the curable liquid.
 8. The method of claim 7, wherein the masking material is removed after the application of the curable liquid coating and prior to exposing the partially enclosed cutting element to the leaching solution.
 9. The method of claim 2, wherein the diameter of the molded sleeve is less than the diameter of the substrate and polycrystalline diamond table.
 10. The method of claim 1, wherein the leaching solution comprises an acid selected from the group consisting of nitric acid, hydrofluoric acid, and mixtures thereof.
 11. The method of claim 1, wherein exposing the partially enclosed cutting element to a leaching solution comprises suspending the cutting element within a leaching solution via magnetic components disposed within the protective element.
 12. The method of claim 1, wherein exposing the partially enclosed cutting element to the leaching solution occurs at least in part under elevated pressure, elevated temperature, or ultrasonic conditions.
 13. A protected cutting element, comprising: a cutting element comprising polycrystalline diamond fixed to a substrate; and a protective element enclosing the substrate and at least a portion of the polycrystalline diamond and exerting a compressive squeeze of about 5-25% on the cutting element.
 14. The protected cutting element of claim 13, wherein the protective element comprises at least one snap ring that exerts the compressive squeeze.
 15. The protected cutting element of claim 13, wherein the protective element comprises at least one material selected from the group consisting of FKM fluoroelastomers, polychloroprene, chlorinated polyethylene, chlorosulfonated polyethylene, epichlorohydrin, fluorosilicone, hydrofluorocarbon, fluoroelastomers, halobutyl elastomers, and FFKM perfluoroelastomers.
 16. The protected cutting element of claim 15, wherein the protective element comprises at least one material selected from the group consisting of FKM fluoroelastomers and FFKM perfluoroelastomers.
 17. The protected cutting element of claim 13, wherein the protective element comprises a pre-molded sleeve that exerts the compressive squeeze.
 18. A method of treating a cutting element, comprising: providing a cutting element comprising polycrystalline diamond attached to a substrate; enclosing the substrate and at least a portion of the polycrystalline diamond within a protective element comprising at least one FFKM perfluoroelastomeric material to form a partially enclosed cutting element; and exposing the partially enclosed cutting element to a leaching solution so that at least part of an unenclosed portion of the polycrystalline diamond is in contact with the leaching solution.
 19. The method of claim 18, further comprising using a snap ring to secure the substrate and at least a portion of the polycrystalline diamond cutting table within the protective element.
 20. The method of claim 18, wherein the protective element is a pre-molded sleeve. 